Re: [PATCH 1/4] drm: add picture aspect ratio flags

Sharma, Shashank
2016-08-04T13:15:43Z

Regards

Shashank

On 8/4/2016 5:04 PM, Emil Velikov wrote:
> On 4 August 2016 at 11:16, Sharma, Shashank <shashank.sharma@intel.com> wrote:
>> Hello Emil,
>>
>> Thanks for your time.
>>
>> I have got mixed opinion on this.
>>
>> IMHO we should expose them to userspace too, as UI agents like Hardware
>> composer/X/Wayland must know what does these
>>
>> flags means, so that they can display them on the end user screen (like
>> settings menu)
>>
>> But few people even think thats its too complex to be exposed to userspace
>> agents.
>>
> If we want these/such flags passed between kernel and user space one must:
> - Provide a kernel interface how to do that
> - Provide a userspace (acked by respective developers/maintainers)
> that the approach is sane and proves useful.
>
> Since the above can take some time, I'd suggest dropping those from
> the UAPI header(s)... for now.
>
> -Emil
Please guide me a bit more on this problem, Emil, Daniel.
The reason why I want to pass this to userspace is, so that, HWC/X/any
other UI manager, can send a modeset
which is accurate upto aspect ratio.

Please think of this complete scenario:
- HDMI compliance testing is going on, and we need to apply a CEA mode
(for example, VIC=3, mode - 720x480@60Hz aspect 16:9)
- But HWC doesnt pass the aspect ratio information, and passed only
720x480@60Hz
- Kernel gets the first matching mode, from edid_cea_modes, which is
VIC=2 720x480@60Hz (aspect 4:3)
- Kernel does the modeset of VIC = 2, and AVI IF contain VIC=2
- Compliance equipment expects VIC = 3, so fails the test case.

In this case, its essential that the userspace, which is triggering the
modeset, must know about the aspect ratio field too.
So does this make it a reason to pass this information to usp ?

Regards
Shashank